The basic principle of bleeding ATV brakes is actually quite straight forward. But getting the brakes to bleed properly may sometimes be easier said than done. This post addresses the most common reasons why your ATV brakes won’t bleed and how to fix them.
You always get the best result from combining these methods to ensure all of the air is out of the system.
1. There is air trapped in the banjo bolt
The standard brake bleeding methods will usually eliminate all of the air trapped inside the actual brake lines. But air may still be trapped inside the connector that attaches the brake line to the master cylinder, often referred to as “a banjo bolt.”
To relieve this air, you need to hold the hand lever in the engaged position and then briefly loosen the nut holding the banjo in place.
Tighten the nut before the lever bottoms out. I recommend using a rag to soak up the brake fluid that squirts out so that it won’t damage the paint on your bike.
2. Not enough fluid being pumped from the master cylinder
The master cylinder on ATVs and the piston inside it are relatively small compared to the one you find on a car on any other larger vehicle. Because of its small size, it can only pump a relatively small amount of brake fluid with each pump.
This makes the standard method of bleeding brakes work less efficiently on smaller brake-systems found on ATVs, UTVs, dirt bikes, motorcycles, or snowmobiles.
The amount of fluid being pumped may not be enough to move the bubbles of air out before you bottom out and have to start a new pumping cycle.
3. The brake shoes are not adjusted properly
Before you attempt bleeding your hydraulic drum brakes, you need to make sure the brake shoes are properly adjusted. If they are not snug, you will never get a good brake feel.
Adjust the shoes according to factory specifications. The adjuster on each side needs to be adjusted equally, and the brake shoes need to be rubbing the drums quite a bit.
You should feel a noticeable drag when you turn the hub. If they are just barely scraping, you may have problems bleeding the brakes properly as the slave cylinder won’t be able to push the shoes far enough.
4. There is a leak somewhere in the brake system
Even the smallest leak may be enough to prevent you from achieving firm brakes. Check the whole system with a dry paper towel, and address any found leaks.
5. There is air trapped in the master cylinder
To remove the air trapped inside the master cylinder, you need to perform a bench bleeding procedure.
The process of bench bleeding the master cylinder is a bit more comprehensive than just standard brake bleeding, but sometimes it is necessary to remove the air trapped inside.
If you happened to run the brake fluid reservoir dry or have replaced or rebuilt your master cylinder, there is a good chance air trapped in the master cylinder is the cause of your problems.
I’ve dedicated a separate post on how you may bleed the master cylinder.
6. The master cylinder is bad
If you struggle to get the fluid down the brake lines, chances are your master cylinder has gone bad.
Inside the cylinder, you find a plunger with an o-ring that tends to wear or go bad over time. If you need several pumps to achieve firm brakes, this further enhances the likelihood of your master cylinder gone bad.
Luckily you can rebuild an old master cylinder, and the parts needed do not cost much. Most manufacturers sell kits that fit your specific unit where step-by-step instructions are included.
7. Incorrect handle installed
If you happened to replace your brake handle/lever recently, it might be what is causing you trouble.
Installing an aftermarket or the wrong type of lever may prevent the piston inside the master cylinder from returning completely when the lever is released.
This may, in turn, prevent the brake fluid from flowing down and in front of the piston. The piston will move, but it won’t get any fluid from the reservoir to pump down the brake lines.
8. Missing copper washers by the banjo bolt
If you have opened the banjo bolt previously, make sure you installed it correctly with one copper or aluminum washer on each side.
If assembled incorrectly, you may have problems building up the pressure, or you may suck air into the brake system each time you pump the brakes.
9. Clogged brake line or bleeder screws
Over time, your brake lines may get clogged from corrosion and debris. If you cannot press one single drop of fluid out of an open bleeder-valve, or if the brake fluid flow is weak, you may have a clogging issue.
Try disconnecting the banjo connector from your master cylinder and pump the brake to see if the cylinder is working properly. Use a rag to prevent the corrosive brake fluid from ruining your paint and plastic.
If you get a firm squirt of brake fluid when you press the brake lever, the clogging is likely somewhere in your brake line.
Before you begin replacing brake lines, it’s worth completely removing the bleeder valve to see if this clears things up. Replace clogged bleeder valves with new ones. Bring the old one, and any automotive store should have new ones at almost no cost.
Additional tips for stubborn brakes that will not bleed
I’ll finish off with many last resort tips to try if your brakes seem to be in good shape but do not want to bleed.
Leave the brake lever engaged overnight
A simple trick to try out if you have tried everything and do not want to start messing with the master cylinder is to zip tie or rubber band the lever in the engaged position overnight.
If you are lucky, this may be all it takes to let the most stubborn bubbles of air escape up into the reservoir tank.
Slowly pump the brakes with the master cylinder cover off
Here is one more simple trick to try before you attempt a complete master cylinder bleed.
Open the brake fluid reservoir cover. With the reservoir topped off with brake fluid and all the bleeder valves closed, slowly begin pumping the brakes. Note if you see any bubbles appearing in the reservoir.
Continue pumping until there are no more bubbles. Reinstall the cover and test your brakes.
Gravity bleed the brakes
Gravity bleeding is a well know method to try when everything else fails. It may or may not be effective. The only way to find out is to try it out.
- Start by removing the brake fluid reservoir cover, and top it off with fluid.
- Put trays under each brake caliper and open the bleeder valves.
- Leave the system for about 20 minutes. Just make sure the reservoir does not run dry, or you will be in for a much harder bleeding job.
- Add more fluid when it is starting to run low.
- Brake fluid will drip out slowly through the bleed valves. Hopefully, the air will come out with the fluid as well.
- After topping off the reservoir a few times, you may try tightening the bleeder valves, replacing the reservoir cover, and see if the brakes have improved.
The brakes will still not bleed!!
If you have reached this point and still had no success bleeding your brakes, I salute your willpower!
Try over-filling the brake fluid reservoir
One time when I had no luck bleeding the brakes on my KTM EXC dirt bike. I tried everything and used bottle after bottle of brake fluid. The brakes were still soft.
Then I tried topping off the brake fluid reservoir completely before continuing manually pumping and bleeding the brakes. And what do you know, after just a few pumps, the brakes were rock solid again.
I cannot explain how it happened, but consider giving it a shot before giving up and taking your machine to the dealer.